1. School of Geography and Geosciences, University of St Andrews, Irvine Building, North Street, St Andrews, Fife KY16 9AL, UK
2. Present address: Ocean and Earth Sciences, University of Southampton, National Oceanography Centre, Southampton, European Way, Southampton, UK
3. Department of Physical Geography and Quaternary Geology, Stockholm University, Stockholm, Sweden
4. Present address: Environmental Change Research Centre, Department of Geography, University College London, Gower Street, London WC1E 6BT, UK